A research team led by Prof. ZENG Jie and GENG Zhigang from the University of Science and Technology of China (USTC) of Chinese Academy of Sciences (CAS), utilized bromide as a reaction medium to spatially decouple the electrolysis process and propylene conversion process in the electrocatalytic oxidation of propylene, achieving efficient electrocatalytic oxidation of propylene to produce propylene oxide. The study was published in the Nature Communications.
Propylene oxide (PO) is a universal raw material for producing various chemicals, including polyether polyols, propylene glycol, and dimethyl carbonate. Recently, the electrochemical synthesis of propylene oxide has attracted widespread attention. Due to limited Faradaic efficiency (<20%), current density (<5mAcm-2), and stability (<10h), the direct electrocatalytic oxidation of propylene to produce propylene oxide is still far from practical application. Although some scholars have made efforts in synthesizing propylene oxide, the Faradaic efficiency is still not satisfactory.
Researchers have spatially decoupled the electrolysis process and propylene conversion process by using a bromide medium. Specifically, Br2 is produced at the anode and then transferred to an independent reactor to react with propylene. The spatially decoupled system avoids direct contact between the anode and propylene, and activity and selectivity are expected to be maintained even at high currents.
In addition, the decoupling system eliminates the interference of a large amount of raw material input on the stability of the system. The electrochemical bromohydrin system can efficiently synthesize propylene oxide using inexpensive carbon paper as an anode. The selectivity of propylene oxide reaches more than 99.9% under all applied potentials.
Schematic illustration of the electrochemical bromohydrin route for efficient synthesis of PO. (Image by ZENG et al.)
Remarkably, a faradaic efficiency of 91% was achieved at 1.9 V vs Ag/AgCl. The system could operate stably for 750 h (>30 days) at a current density of 250 mAcm-2, and the faradaic efficiency exhibited only a decay of 0.73% during the whole process.
An amplified flow-through reactor with a geometric electrode area of 25 cm2 was also designed and combined with an autonomously designed distillation separation device to verify the practical application prospects of the above strategy. After continuous electrolysis for 50 h at a current of 6.25 A, a total of 262 g of propylene oxide pure product was obtained.
In addition, the electrochemical bromohydrin route is also applicable to the efficient conversion of other alkenes, including gaseous alkenes (such as ethylene, 1-butene, and isobutene) and liquid alkenes (such as 1-octene, cyclopentene, and styrene).
These results confirm the industrial viability of the electrochemical bromohydrin route to epoxides.
Paper link：https://doi.org/10.1038/s41467-024-48070-1
(Written and edited by HUANG Rui, USTC News Center)
